Re: Shearing Interferometer with Ti-Sapph

Posted by on Sep 21, 2016; 4:28am
URL: http://confocal-microscopy-list.275.s1.nabble.com/Shearing-Interferometer-with-Ti-Sapph-tp7585684p7585685.html

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Here's a shot in the dark here for you, since I have never tried doing what you asked about.

Short pulse lasers only interfere over a short distance called their coherence length. It might only be 10-30 microns or so depending on the laser's bandwidth. If the path length difference of the two interfering beams is more than this 10-30 microns, then no fringes.

If the interferometer works by beam 1 reflecting off the front of the glass wedge (going through no glass) and beam 2 reflecting off the back surface of the glass at a little different angle (going through the glass twice), then the optical path length of beam 2 is quite a bit more than that of beam 1. Probably by much more than 10-30 microns since the wedge is probably at least 1 mm thick where you use it. I would guess no fringes.

Basically, I am asking whether your interferometer is designed for short pulse lasers. I bet the Thorlabs folks could weigh in on it if you email them.

Anyway, isn't it easier to check collimation by shooting the beam across the room and checking the diameter is constant?

On Tue, Sep 20, 2016 at 9:07 PM, Tim <[hidden email]> wrote:

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Hello, we recently purchased a shearing interferometer from Thorlabs (Part # SI254) to test collimation after beam expansion in our two-photon microscope setup. The strange thing is we cannot seem to get an interference pattern either before or after beam expansion (varying the distance between the lenses in the beam expander). We do see the pattern clearly if we try on a simple laser diode. Does anyone have experience looking at the shearing interferometer pattern with a Ti-Sapphire laser or have any ideas what may be causing our problem?

Thanks for any help,
Tim

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